|PAUL, CHANDRA - University Of Illinois|
|MOTTER, HELDER - Universidade Federal De Vicosa|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2019
Publication Date: 11/13/2019
Citation: Paul, C., Motter, H.Z., Walker, D.R. 2019. Reactions of soybean germplasm accessions to six Phakopsora pachyrhizi isolates from the United States. Plant Disease. 104(4):1087-1095. https://doi.org/10.1094/PDIS-09-18-1704-RE.
Interpretive Summary: Soybean rust is one of the most economically important diseases of soybean worldwide, and fungicides are used heavily to reduce yield losses. Resistant soybean varieties would help to reduce fungicide applications and expenses. Genetic resistance has been identified in more than 120 soybean germplasm accessions, but due to substantial diversity in the pathogen, individual resistance genes do not provide resistance to all strains of the rust fungus. This study identified seven Asian soybean lines that have resistance to six strains of soybean rust from the southern United States, and several other lines that are resistant to most of the six strains. This knowledge can be used together with information from recent gene mapping studies to guide soybean breeders in deciding which resistance genes should be combined to develop new soybean varieties that are likely to have broad and durable resistance to soybean rust.
Technical Abstract: Soybean rust, caused by Phakopsora pachyrhizi Syd. & P. Syd., is one of the most economically important foliar diseases of soybean. Resistant cultivars would reduce yield losses and management costs, but considerable pathogenic diversity exists among populations of the fungus, so resistance to a range of pathotypes is essential. Seedling and detached leaf assays were conducted to better characterize the resistance of 41 soybean plant introductions (PIs) to six purified isolates of P. pachyrhizi originating from the southern United States. Seven accessions with unknown resistance genes and three differential lines with mapped Rpp genes were resistant to all six isolates, including two Florida isolates that were able to defeat resistance conditioned by the Rpp1 through Rpp4 genes. Several other PIs were resistant to four or five of the six isolates. Many of the resistant accessions have subsequently been reported to have a resistance allele at the Rpp3 locus, and two others have resistance genes at the Rpp4 or Rpp6 loci. This study provided details about resistance reaction phenotypes that can be useful for understanding mechanisms of resistance and which Rpp genes and alleles could be combined to obtain broader and more durable rust resistance in soybean cultivars.